Significant increase in the efficiency of electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources in tandem mass spectrometry (MS/MS) will have a profound impact on single cell MS-based analysis and the entire analytical field of characterization of proteins, lipids, and metabolites. Almost 100% ionization efficiency of nanoflow ESI (APCI) sources makes it a unique analytical tool specifically applicable to the MS-based analysis of zeptomole amounts of chemical and biological substances. We plan to build a platform combining subatmospheric nanoflow ESI and APCI sources and very efficient ion collector to drastically improve sensitivity and speed of MS-based identification of miniscule amount of biomaterials harvested from single cells.